Mold injection machines now in common use and as shown in U.S. Pat. No. 3,600,755 generally include a reciprocating feed screw for supplying a shot or charge of an injection material to a metering unit for injection into a mold. In these machines, the material is usually loaded into a metering chamber when the screw is rotated and then moved from such chamber into a discharge or accumulating chamber, by axial displacement of the screw, for injection into a mold. These machines are not only relatively bulky and expensive but are limited in operation to a set charge of material so as to produce similar articles in volume. In other words, they are incapable of varying the material charge to inject varying volumes of material into successive molds to produce articles of varying shapes and sizes. Additionally these machines, even in production runs, require excessive set up time and equipment. A further disadvantage results in the residence time of the material in the machine. Thus, when material is not continuously moved in a single direction, the injected material includes portions of varying residence times within the machine so as to impair the quality and/or the appearance of the finished article.
In U.S. Pat. No. 3,723,037, a vertical screw is supported for rotatable and vertical axial movements in a metering housing. Rotation of the screw feeds material from the hopper into a metering housing concurrently with moving the screw upwardly. The nonrotated screw is then axially moved to force the material from the housing into a transfer cylinder from which only a part of the transferred material is injected into a mold.
The feed screw of the injection machine shown in U.S. Pat. No. 3,020,591 is rotatably supported in a cylinder of an injection piston. Along with being rotatable, the feed screw is also axially movable. The end of the cylinder adjacent the free end of the feed screw forms a storage chamber the volume of which may be varied by varying the axial movement of the feed screw relative to the cylinder.
The injection machine in U.S. Pat. No. 3,327,354 has an injection portion or head that includes a rotatable feed screw and an injection nozzle that are movable as a unit relative to a carousel mounted mold. The feed screw extends horizontally and is held against axial movement relative to the injection nozzle. To fill a mold, the injection head is moved as a unit toward the mold to operatively engage the nozzle with the mold. The screw is then rotated to directly move injection material through the nozzle and into the mold, after which the screw is stopped or idled. The injection head is then retracted from the mold to permit another mold being moved into a mold filling position.